FAMILY STUDIES IN NARCOLEPSY

Out of a population of 188 unrelated narcoleptic probands, we identifi ed 14 probands (7.44%) with a family history of narcolepsy, 23 (12.23% ) with a family history of isolated repeated episodes of naps and/or l apses into sleep and 151 (80.31%) without a family history of either c ondition. Clinical, polysomnographic or zygotic differences could not be evidenced in the three groups. Empirical risk for narcolepsy was 40 .7 times greater among first-degree relatives of narcoleptics than in the general population. Narcolepsy and the condition characterized by isolated repeated episodes of naps and/or lapses into sleep have a com mon genetic component. This finding has important implications. Indeed , when the latter condition is included in the spectrum of narcolepsy, the empirical risk figure is relatively close to that expected in cas es of simple mode of inheritance. A trend in favor of a more frequent transmission through mothers than fathers is emphasized.